A problem with this kind of networking of devices or bus stations with each other, however, is the possibility for monitoring or diagnosing the system in the case of a malfunction or for optimising the system. There is thus a need to monitor such bus systems, to diagnose malfunction conditions and to allow or facilitate optimisation of the bus system.
In U.S. Pat. No. 4,817,080 A a monitoring system for a local area network has a distributed organization, in which a monitor manager on the network receives information from individual monitor units connected to different buses of the local area network. Each monitor unit employs a plurality of counters in a packet memory that are dynamically allocated to specific packet characteristics as new packet characteristics appear on the network. A look-up table contains the association between counters and the characteristics with which they are associated, and a look-up engine operates the look-up table in such a manner as to enable it to search for the location of specific counters by employing a binary search method. In this way, all processing for a given packet can be performed within the minimum packet time.
JP 05 130 108 A discloses a bus type local area network monitor equipment. The purpose of this monitor equipment is to connect monitor and control for a bus type local area network even when a tap transceiver connecting to a bus type local area network monitor is not available due to a fault or the like. The known monitor is provided with tap transceivers connected to a bus, plural interface circuits exchanging monitor information and control information of the bus type local area network and a selection circuit selecting one interface circuit optionally from the plural interface circuits. The monitor and control of the bus type local area network are implemented by sending/receiving the monitor information and the control information of the bus type local area network via the tap transceivers selected and connected by the selection circuit.
FR 2 691 029 A1 refers to remote surveillance and maintenance for digital transmission systems. The network interconnects to subscriber terminals with other subscriber terminals, by two bus networks. Two terminals are interconnected by a communication network. Two network terminals control operations. A remote testing of protocol carried out by an analyser connected to one of the terminals by a bus network, and by the addition of a specialist terminal to sample the protocol. The advantage of such a remote surveillance and maintenance appears to be that remote testing of network does not need qualified personnel or could not to go to side, and therefore is cost effective. Such a method serves also to transport protocols for example X25 and to ISO/OSI. A bus monitor circuit for switching system and a method for monitoring is disclosed in EP 0 601 768 A2. Here, a bus interface is connected to a data bus for receiving a copy of every packet on the data bus. An error detector determines whether the received packet contains an error, and produces an error detect signal and an error check result, if the receiver packet is determined as having an error. In response to the error detect signal, the received packet, the error check result and time-off-day data are stored into a register and transfer to one of the storage locations of a memory to keep a list of error records. A maintenance station reads stored error records form the memory for identifying the source of errors. WO 96/38792 A1 discloses an apparatus for monitoring and controlling data flow in a computer network device having a plurality of parts comprising control means for directly linking ports together on the basis of additional information stored in the control means whereby incoming packets are lined directly to an output port to achieve high performance. The additional information is stored in one or more look-up tables in addition to the normal CAM with the or each table addressed by separate processing. This allows the implementation to be in hardware rather than in software.
WO 98/14852 A1 discloses an interface between a remote communication network and a process control system. The interface includes a storage device, a communication software stack and a user software layer. The user software layer enables interfacing between the remote communications network and the process control system by directing the communication software stack to operate into process control system using a process communication protocol, by monitoring the message traffic on the communication software stack, and by copying requested message traffic to the storage device. The user software layer also includes media interface software that allows access to the storage device by the remote communications network to deliver specific data to a device connected to the remote communications network. WO 00/52579 A1 discloses a bus system with a master and several slaves which are linked by a bus line. Between the master and the slaves at least one repeater is inserted. According to the unit disclosed therein, a monitoring unit is connected to the bus line which detects and evaluates the reaction times between sending a master call and the receipt of a slave response. In DE 198 52 276 A1 a method for receiving a message via a serial data bus is disclosed. The method involves monitoring the data bus to identified start information for a first sub-message, receiving the first sub-message, starting a timer at the start of reception of the first sub-message; comparing the timer actual value of a first threshold value and monitoring data bus for the presence of the further start information of a further sub-message if a certain timer criterion is fulfilled. This document refers also to a functional unit for receiving messages over a serial data bus and a local network with functional units. In EP 1 049 292 A2 a system and method for network monitoring is disclosed. An algorithmic snoop unit snoops interleaved transactions over a shared bus as data is transmitted via transactions between clients coppered to shared bras, and executes various algorithms upon data snooped from the transactions. The unit includes one or more algorithmic entries along with an algorithmic engine. Each algorithmic entry includes a client ID register that identifies the client associated with a transaction, a starting address register and an ending address that de fine the address range upon which an algorithm will be executed, a read or write flag that identifies whether the transaction is a read or write operation, an encryption key register for holding an encryption key, a decryption key register for holding a decryption key, and algorithm ID register for identifying an algorithm to be executed, a status-control register which holds various status and control, an accumulator for accumulating results from the execution of the algorithm, a temporary storage area, and one or more memory pointers that index a location in memory for results comprising a large amount of data. If a match is found, the algorithm identified by the algorithm ID register is executed upon the data carried by the transaction. Furthermore, JP 2 002164899 A discloses a network monitoring method and its equipment. The problem to be solved is to provide a network monitoring method and its equipment for finding and taking a countermeasure against disguise of a device. To solve that problem the network monitoring equipment is provided with a topologic memory part which stores topological information of the network, a response time memory part which stores obtained response time of the execution of response inspection command, and a decision part which decides the consistency between topological information stored in the topologic memory part and the response time stored in the response time memory part, and it finds and takes a countermeasure against disguise of a device in the network like IEEE 1394 by which such topology can be obtained.
If in such bus systems there are communication problems between one or more sensors or actuators and the control unit, the analysis of such problems involves considerable complexity, if a problem of this sort can be solved at all. In these instances a conventional multipurpose meter is only rarely able to provide information on the cause of a faulty communication. Often the only remaining possibility is to carry out monitoring or diagnosis of the bus system using additional external, often very expensive, equipment. For this purpose, often so-called bus monitors are connected to the bus system as purely passive and external devices in order to facilitate monitoring or diagnosis in the case of a malfunction.
The bus monitor is a relatively passive device and does not actively participate in the communication of the bus system. Its task is rather to “listen in” to any data traffic of the bus system and to store it in a memory dedicated for this purpose. In order to be able to find and identify the thus stored data at a later time of diagnosis, each individual data telegram is stored in the memory of the bus monitor with a time stamp and/or an index. Often such bus monitors have their own display or screen allowing to display directly and on-line the detected data traffic. In principle, there is also the possibility to retrieve the data previously recorded and stored in memory in order to analyse them off-line at a later point in time.
Such bus monitors also often comprise a filter function allowing complex systems in particular to pre-sort and store the telegram traffic of the bus system according to certain filtering criteria. With such filters an essential distinction is made between “on-line filters” and “off-line filters”. An on-line filter is a filter that evaluates the telegrams established on the bus system already during recording—i.e. on-line—however, records only those which fulfil a certain filtering rule. The advantage of an on line filter is a reduction of the data volume to be stored; a disadvantage is, however, that possibly relevant telegrams are lost in the filtering process, resulting in incomplete recordings. Off-line filters, on the other hand, are filters that analyse data from previous recordings, allowing the data to be presented in a more structured manner. The advantage of such off-line filters is that only the data can be presented that are interesting at the moment of analysis; if needed, however, an overview over the entire data may also be selected. A disadvantage of such off-line filters is that they always cause very high data volumes.
As mentioned above, the previously described bus monitors must be connected as additional devices to the existing bus system. By externally connecting these bus monitors to the bus system as passive devices, there is a danger that, as a side effect, they will influence the bus system as a consequence of changed electrical characteristics of the overall system, which can then lead to faulty diagnoses.
A further disadvantage of such external passive bus monitors is that they cannot achieve long-term diagnoses since they cannot continuously remain within the bus system. Extensive trouble shooting is therefore often not possible since the bus monitors are not integrated in the bus system at the point in time when a malfunction occurs.
Moreover, such external bus systems are not suitable for error diagnosis because they only detect the local data traffic at the place where the bus monitor is connected. Global monitoring, however, is not possible. Each individual bus station's data traffic behind its bus interface is therefore not detectable by an external bus monitor, i.e. malfunctions in the communication within the bus station remain undetected.